The Honda six-cylinder made its debut at Monza in September,
1964. The motorcycle had been designed to make life difficult for the Yamaha 250
RD 56.
The 250 RD 56 had four fewer cylinders, but in the able hands of Phil Read it
had outdistanced Jim Redman with his Honda. Nevertheless it was clear that a
tougher driver with an improved six-cylinder would lead the field the following
year. So the Yamaha company built a four-cylinder 250 but kept it a secret
almost until its first appearance, which co-incidentally took place at Monza in
1965.
Yamaha was unlucky at Monza. Rain poured down relentlessly, and the new
two-stroke engine had a lot of trouble with carburetion.

So it was all off for Yamaha until the 1966 season. Despite
the engine's remarkable power, Read never managed to get the most out of it
because of serious problems involving maneuverability and weight. He was the
eternal second in 1966. In 1967 Read and Yamaha had their first wins, and so did
teammate Bill Ivy. The four-cylinder Yamaha was the fastest 250 that had ever
appeared on a track, but it was not yet the most competitive vehicle in its
class.
But in 1968 the Yamaha came into its own. That year Mike Hailwood and Ralph
Bryans with their Hondas—no longer the frightening machines they had once
been—had to step aside for Phil Read. All he had to do with his over-60-h.p.
Yamaha was beat Ivy.

Then the FIM decided to limit 125-cc. and 250-cc. engines to
two cylinders, and Yamaha made the first of several withdrawals from racing. At
the time the four-cylinder 250 was the most advanced racing motorcycle around.
That year's model weighed some twenty pounds less than the prototype that had
debuted at Monza and had a little more horsepower. It could go extremely fast
for a 250. In a clocked leg of the Tourist Trophy it had run at some 150 m.p.h.,
which meant that it could go even faster in other conditions. This made it
competitive with some of the finest 500-cc. motorcycles.

In 1967 Yamaha developed a 125-cc. model from the
four-cylinder 250. The 125 was designed to replace the two-cylinder RA 97, which
had won several Grand Prix races in 1966 but had failed to take the world title.
It was a daring job for two reasons: Nobody before had tried to build a
four-cylinder, two-stroke 125, and nobody before had derived a small vehicle
from a larger one, but rather the reverse.
The four-cylinder 125 was water-cooled and used rotating-disk distribution. It
generated 35 h.p. at 18,000 r.p.m. in the prototype. And it seemed to be a sound
racer. Bill Ivy rode this first model to win the 1967 world championship.

Despite the superiority of the four-cylinder 125, the Yamaha
people were fully aware of the threat of the five-cylinder Honda 125's return,
and they had heard talk about a six-cylinder version. The Yamaha technicians
worked hard on the engine and managed to get another 7 h.p. out of it. Read and
Ivy had a pair of two-wheelers that could deliver really exceptional
acceleration and speed for their size. The 125 became a bone of contention
within the Yamaha team. Read had never managed to ride the 250 to victory over
Hail-wood's six-cylinder Honda, and Ivy kidded him about it. Read won in the 250
class in 1968 and decided to go after the title earmarked for Ivy as well. Phil
Read succeeded, winning the championship with the four-cylinder Yamaha. He was
dismissed from the team at the end of the season

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